1. Field of the Invention
The present invention relates to systems and methods for feeding and transporting documents and to detecting a document trailing edge.
2. Background Art
A typical system for feeding and transporting documents includes a feeder and a separator in the document feeding portion of the system, and a series of roller pairs or belts in the document transporting portion of the system. In the feeding portion of the system, the feeder acts with the separator to feed documents singly, in order, from a stack. In the transporting portion of the system, the roller pairs and/or belts convey the documents, one at a time, past other processing devices such as readers, printers, and sorters that perform operations on the documents. The feeder is typically a feed wheel, but may take other forms. The separator may be a wheel, but also may take other forms such as a belt. Further, the components in the transporting portion of the system may take a variety of forms. The systems also include a component in the document feeding portion of the system that nudges documents into the nip between the feeder and the separator. A suitable nudger may be a nudger wheel, but may take other forms. An existing document feeder is shown in U.S. Pat. No. 6,199,854. That patent describes a document feeder with a variable speed separator.
In existing systems for feeding and transporting documents, operations that depend on the position of the document are generally performed in the transport stage, or transporting portion of the system. For example, U.S. Pat. No. 5,848,784 describes a document separation apparatus. That patent describes the downstream acceleration/deceleration of documents with pinch rollers to adjust document spacing. U.S. Pat. Nos. 5,419,546; 5,437,375; 5,439,506; 5,509,648; 5,671,919; and 5,908,191 describe examples of other document operations.
Workers will understand the importance of detecting the leading and trailing edges of documents, and the gaps between them, as they pass through the feeding system and the transport system beyond. Many operations to be performed upon the documents (for example, printing, reading, imaging and so forth) are required to be performed at specific locations along the length of the document, and so it is very important for the system to be able to detect when the leading or trailing edge of a document appears at a specific point. From this data, the system can extrapolate its necessary understanding of where the document is, how fast it is traveling, and when and where specific operations should be performed upon it.
Similarly, it is just as important for the system to understand the lengths and locations of gaps between documents as it is for it to understand the lengths and locations of the documents themselves. It will be understood that document processing systems seek to produce the highest possible throughput rates, and therefore, workers seek to minimize gaps between successive documents. At a given transport speed, a gap is a unit of time in the operation of the system which is not occupied by a document, and is therefore lost to productive processing. At the same time, systems often require a discrete and controlled time interval between documents, for example, to transmit data gathered from the previous document, or to reset mechanisms after processing the previous document, and the optimum gap is usually dependent upon the length of the previous document. The longer the previous document (generally speaking) the longer the gap required after it before the system can be ready to commence processing the next document.
Workers therefore always seek to reduce the gaps between documents to the smallest possible consistent with all system functions, and for system functions, gaps are most usually dealt with as time measurements rather than measurements of physical distance. In order to best measure and manage both document lengths and the gaps between them for the optimum throughput, workers will understand that it is advantageous to be able to detect both leading and trailing edges of documents as early in their processing as possible, and preferably, during the feeding process, before any other processes are to be performed upon them.
Ideally, such a system would measure the position of the edges of the document in the feed hopper even before it is fed. However, documents can vary widely in overall length. For example, if we consider a high-speed document processing machine such as the Unisys NDP2000, the specified range of document length is 4.25xe2x80x3-9.25xe2x80x3, or a range greater than 100% between shortest and longest. There is a need to detect trailing edges of unequal length documents, while in motion, before documents leave the feeder area to sense for overlapping and aid in controlling spacing between documents. To meet this need a detector capable of detecting over a wide possible range of document trailing edge positions would be required. It is found that a single detector, at a suitable fixed location in the feed hopper consistent with the shortest possible document length, serves the desired function.
In order to perform operations on documents that depend on document position, leading and/or trailing document edges are detected depending on the operation to be performed. A known device for detecting document edges is the photo edge detector. U.S. Pat. No. 5,848,784 describes the use of an edge detector. The edge detector is suitable for some applications, but may be sensitive to, for example, printing on the documents and/or document thickness and/or opacity. There is a need to overcome the optical sensor""s inability to differentiate between the trailing edge of documents and printing, fold lines, holes or other document characteristics that look like a document edge.
Workers will understand that photo edge detectors can be and are used to detect both leading and trailing edges of documents, but they can only function upon individual documents, for example when traveling singly in a document track. Since they rely for their function upon the interruption of a beam of light, traditional photo edge detector applications are unsuitable for use in a feed hopper which contains many documents in a stack because the document trailing edge may be difficult to identify particularly against the document stack and other document characteristics that look like a document edge. Such sensors in traditional applications have been used to detect leading edges of documents as they leave the stack in the feed hopper, but cannot be used to detect trailing edges until the trailing edge has entirely separated from the stack of documents behind it in the feed hopper.
For the foregoing reasons, there is a need for an improved system and method for feeding and transporting documents that detect a document trailing edge at a known location with a photo edge detector while it is still within the feed hopper.
It is, therefore, an object of the present invention to provide an improved system and method for feeding and transporting documents that detect, based on a photo edge detector, a document trailing edge at a known location within a feed hopper, while the document whose trailing edge is to be detected is still in the process of being fed from the stack of documents behind it.
In carrying out the above object, a system for feeding and transporting documents is provided. Each document has a leading edge and a trailing edge. The system comprises a feeder stage, a photo edge detector and a transport stage. The feeder stage includes a hopper, a feeder and a separator. The feeder acts with the separator to feed documents singly, in order, from a stack of documents in the hopper. The hopper includes a hopper wall extending toward the feeder with a waterfall step along the hopper wall and with the stack of documents engaging the hopper wall including the waterfall step to form a pocket area. The pocket area is formed over a limited distance extending from the waterfall step along the hopper wall toward the feeder. The photo edge detector is located in the pocket area and faces the stack of documents such that a feeding document slides between the stack of documents and the hopper wall. The feeding document trailing edge passes the waterfall step and is detected by the photo edge detector while in the pocket area. The transport stage is downstream of the feeder stage for receiving the fed documents.
By adding a waterfall step in the hopper wall at a specific height and an optical sensor at a specific distance from this step, a void or pocket area is created where documents in the stack are outside of the optical sensor""s viewing range. As the trailing edge of the fed document clears the step, it snaps down into viewing range of the sensor signaling the trailing edge without adding unwanted drag on the document. Advantageously, this technique does not require additional moving mechanical parts or opposing forces on the documents as they move toward the feeder in the hopper. The photo edge detector may suitably be implemented as a single optical sensor, however, an array of photo edge detectors could alternatively be located in the pocket area. The array would provide more information for determining the feeding document trailing edge position and would accommodate documents of varying thicknesses that result in pocket areas of varying sizes.
At a more detailed level, the present invention comprehends control logic in communication with the photo edge detector or detectors for determining the feeding document trailing edge position based on the photo edge detector or detectors, and a control device. The control device performs a document processing function in response to direction from the control logic.
Further, in carrying out the present invention, a method for feeding and transporting documents is provided. Each document has a leading edge and a trailing edge. The method comprises providing a feeder stage, providing a photo edge detector, and providing a transport stage. The feeder stage includes a hopper, a feeder and a separator. The feeder acts with the separator to feed documents singly, in order, from a stack of documents in the hopper. The hopper includes a hopper wall extending toward the feeder with a waterfall step along the hopper wall and with the stack of documents engaging the hopper wall including the waterfall step. This forms a pocket area over a limited distance extending from the waterfall step along the hopper wall toward the feeder. The photo edge detector is located in the pocket area and faces the stacked documents. A feeding document slides between the stack of documents and the hopper wall with the feeding document trailing edge passing the waterfall step and being detected by the photo edge detector while in pocket area. The transport stage is downstream of the feeder stage for receiving the fed documents.
At a more detailed level, the method may alternatively utilize an array of photo edge detectors located in the pocket area and includes the steps of determining the feeding document trailing edge position based on the photo edge detector(s) and performing a document processing function in response to the feeding document trailing edge position.
The advantages associated with embodiments of the present invention are numerous. For example, embodiments of the present invention detect a document trailing edge at a known location by sensing the document trailing edge with an optical sensor. Embodiments of the present invention are suitable for use in a feed hopper. Detecting the trailing edge position while the document is still in the feeder allows operations to be performed on the document, as well as other operations to be performed while the document is still in the feeder. In addition, knowing the trailing edge position allows a system to know when to perform operations on subsequent documents. Many document processing products could benefit from embodiments of the present invention. For example, copiers, fax machines, sheet feeders for computer printers, automatic teller machines, and document image scanners are just a few examples of products that could benefit from embodiments of the present invention.